Question

Bromide is converted into ethane by heating it in an ether medium with: (a) \(\mathrm{Al}\) (b) \(\mathrm{Zn}\) (c) \(\mathrm{Na}\) (d) \(\mathrm{Cu}\)

Short answer

(c) \(\mathrm{Na}\) converts bromide to ethane in an ether medium.

Step-by-step solution

Understand the Reactants

To begin, we need to identify that bromide here refers to an alkyl bromide, such as bromoethane. The question is asking what can convert bromoethane into ethane using heat within an ether medium.

Analyze Wurtz Reaction

The Wurtz reaction is commonly used to couple alkyl halides like bromoethane using sodium (Na) metal in an ether solvent to produce alkanes such as ethane. The equation for Wurtz reaction is: \[ 2RBr + 2Na \rightarrow R-R + 2NaBr \] where \( R \) represents the alkyl group.

Identify Suitable Metal

Given the Wurtz reaction, sodium (Na) is the suitable metal that reacts with bromoethane to form ethane in an ether medium. Aluminium (Al), zinc (Zn), and copper (Cu) are not suitable for this transformation in the given conditions.

Confirm the Solution

Based on the criteria provided and the nature of the Wurtz reaction, the correct answer is to use sodium (Na) to convert bromide into ethane.

Key concepts

Alkyl Halides

Alkyl halides are important chemicals in organic chemistry, known for their reactivity. In Wurtz reaction, bromoethane is an example of an alkyl halide. The molecular structure includes an alkyl group (like ethyl from ethane) bonded to a halogen, such as bromine. Bromoethane can be represented as \(\mathrm{C_2H_5Br}\), where the ethyl group \(\mathrm{C_2H_5}\) is linked to a bromine atom.

Alkyl halides participate in various reactions, making them versatile in organic synthesis. Wurtz reaction capitalizes on their ability to form carbon-carbon bonds by replacing the halogen atom with another alkyl group, leading to the formation of higher alkanes. Additionally:

• They are often used as intermediates in chemical synthesis.
• Can undergo nucleophilic substitution, where the halide is replaced by another group or atom.
• Are less polar than alcohols due to the presence of the halogen atoms.

Understanding how alkyl halides react helps in grasping the mechanics of many organic reactions, including improving the synthesis strategies for complex molecules.

Sodium Metal

Sodium is a key player in the Wurtz reaction, appreciated for its reactivity and ability to donate electrons. It's an alkali metal, often used in reactions that require a reducing agent. In the Wurtz reaction, sodium's primary role is to facilitate the formation of a carbon-carbon bond between two alkyl halides.

This process typically involves a mechanism where sodium forms a radical anion, enabling the coupling of two alkyl groups to form a new alkane molecule. Here's what makes sodium ideal:

• It reacts vigorously with alkyl halides.
• Serves as a powerful electron donor that promotes radical formation.
• Forms an ionic bond with halogens, aiding in their removal from the compound.

When used with other metals like aluminum, zinc, or copper, these metals are less reactive and unsuitable for the same conditions, making sodium an exceptional choice for Wurtz reaction.

Ether Solvent

The choice of solvent is crucial in chemical reactions. In the Wurtz reaction, ether solvent is preferred due to its excellent properties. Ethers are relatively non-polar and provide an inert environment that does not interfere with the reactivity of the metal and the alkyl halides.

In addition to providing a suitable reaction medium, ether solvents like diethyl ether also help to stabilize the sodium metal and prevent unwanted side reactions. Key characteristics of ether solvents include:

• Polar but non-reactive towards organometallic species.
• High boiling points, which support reactions at elevated temperatures.
• Stability under the conditions preferred for Wurtz reaction.

Their ability to dissolve a wide range of organic and inorganic substances makes them valuable in many synthesis processes, offering the perfect environment for efficient alkane formation from alkyl halides and sodium metal.

Alkane Formation

The primary goal of the Wurtz reaction is to form alkanes, specifically through the coupling of alkyl halides. This reaction is advantageous when forming symmetrical alkanes such as ethane in the given exercise. The general reaction path involves replacing the halogen atoms with a carbon-carbon bond between two identical alkyl groups, creating the alkane.

The simplicity of the products—alkanes—makes them significant in organic chemistry:

• Alkanes are saturated hydrocarbons, consisting only of C-C and C-H bonds.
• They are relatively less reactive compared to other hydrocarbons due to the lack of functional groups.
• Provide fundamental materials for further chemical transformation in industrial chemistry.

The Wurtz reaction remains a classic method to synthesize alkanes, making it essential for students to understand both the mechanism and the outcome in terms of molecular structure and properties.